This invention relates to ink dispensers and in particular to ink dispensers in the form of a roller of porous material holding ink within the pores of the material.
Ink dispensers in the form of rollers are used to apply ink to impression faces of type fonts of a printing device for example a drum printer used in postage meters. The drum printer used in a postage meter comprises a rotatable print drum carrying a die plate extending around the peripheral surface of the drum for printing invariable information and a plurality of type wheels, extending through one or more apertures in the die plate, carrying type characters for printing variable data. During printing, the rotatable drum is rotated with the surface of the ink dispensing roller pressed against the impression faces of the die and type characters thereby to apply a layer of ink to the impression faces. After receiving the ink, rotation of the drum brings the inked impression faces into printing engagement with a print receiving surface of a mail item to produce a printed impression on the mail piece.
The ink dispensing roller includes an ink reservoir comprising porous material of cylindrical shape. Initially pores of the material are charged with ink. Rotation of the ink dispensing roller while in engagement with the print drum causes ink to be dispensed from the peripheral surface of the porous material. The ink removed from the peripheral surface of the porous material is replenished with ink drawn from the inner part of the porous material. When the quantity of ink removed from the reservoir results in depletion of ink to an amount which is incapable of fully inking the impression faces of the print drum, the ink dispensing roller is replaced with a fully charged ink dispensing roller. It is advantageous for the ink dispensing roller to contain a sufficient quantity of ink that the ink dispensing roller is capable of use in a relatively large number of printing operations and only requires to be replaced infrequently. In order to permit a sufficiently large amount of ink to be contained in the ink dispensing roller the pores or voids occupy as large a percentage of the reservoir as is practicable. However, while large voids enable a relatively large quantity of ink to be contained in the reservoir, the large voids result in relatively low surface tension effects acting on the ink in the reservoir. Consequently initially ink is released too readily from the large voids so that there is a tendency for too much ink to be applied to the impression faces of the print drum. Also due to the low surface tension effects, when ink is removed from the surface of the ink dispensing roller the surface tension acting on the ink in the pores is insufficient to ensure withdrawal of ink from the inner portions of the ink reservoir so that a significant quantity of ink remains within the reservoir when the ink becomes depleted at the surface of the ink dispensing roller.
To overcome the deficiencies of ink dispensing rollers described hereinbefore and to provide an ink dispensing roller having a substantially uniform and constant rate of dispensing of ink, known ink dispensing rollers have been provided with a layer of material extending over the ink supplying surface of the ink reservoir, the layer of material having pores which are of smaller dimension than the pores of the porous material forming the ink reservoir. The layer of material having relatively small pores acts to meter the supply of ink from the ink reservoir to the external peripheral surface of the ink dispensing roller. Also the smaller pores result in an increased surface tension effect acting on the ink thereby ensuring that an increased quantity of ink is drawn from the pores of the reservoir during use of the ink dispensing roller. With the metering of the ink and improvement of withdrawal of ink from the reservoir, due to the provision of the layer with relatively small pores, ink dispensing rollers can achieve a relatively high number of printing operations before replacement of the ink dispensing roller is required.
In known constructions of ink dispensing device in which an outer layer of material having relatively small pores extends over an outer surface of an ink reservoir having relatively large pores, the layer of material is bonded to the outer surface of the ink reservoir by means of an intermediate layer of adhesive. It will be appreciated that the intermediate layer of adhesive must permit the flow of ink therethrough from the ink reservoir to the outer layer of the ink dispensing device and furthermore the adhesive must be compatible with the ink.
The present invention overcomes the disadvantages of bonding the outer layer to the ink reservoir by means of adhesive.
According to a first aspect of the present invention an ink dispensing roller includes a cylindrical ink reservoir having a peripheral surface, said ink reservoir comprising porous material having a relatively high void content for containing ink; an outer metering layer extending in ink transfer engagement with the peripheral surface of the ink reservoir, said outer metering layer comprising material having relatively small pores and said outer metering layer being effective to dispense ink from an outer ink dispensing surface thereof and to draw ink from said ink reservoir to replenish ink dispensed from the ink dispensing surface; said outer metering layer being provided with elements extending beyond the peripheral surface of the cylindrical ink reservoir adjacent respective end walls of the ink reservoir; and means cooperating with the ink reservoir to secure and maintain said elements located adjacent said respective end walls of the cylindrical ink reservoir.
Preferably the means to secure the elements of the outer metering layer include end cheeks, and the elements of the outer metering layer are clamped between the end cheeks and the ink reservoir.
According to a second aspect of the present invention in a method of manufacturing an ink dispensing roller comprising a cylindrical ink reservoir having a peripheral surface and an outer metering layer of tubular form extending around said peripheral surface of the ink reservoir, the method includes the steps of providing a sheet of porous material having first and second opposite faces and first and second edges extending in spaced parallel relationship respectively along opposite edges of said sheet; said first and second edges intersecting with said first face along first and second lines respectively; bringing first and second areas of the first face of the sheet adjacent said first and second lines respectively into face to face contact with the first and second lines aligned with one another; effecting welding to join the sheet along said first and second lines and thereby form the sheet into a metering layer of tubular form and locating the metering layer of tubular form to extend around and in ink transfer engagement with the peripheral surface of the ink reservoir.
Preferably after the welding step the tubular form is manipulated so that the face becomes a radially exterior surface of the metering layer of tubular form.
If desired, welding is effected along a relatively narrow region of the first and second edges and after said welding additional material is welded to the first and second edges to form a reinforcing bead extending between the first and second edges.